Modem communication receivers are often required to operate over a large dynamic range. A typical prior art receiver architecture is shown in prior art FIG. 1. Many times in order to comply with the system dynamic range requirements, a receiver will incorporate gain controllable amplifiers to adapt the receiver gain to a wide variety of signal conditions. Those skilled in the art will recognize that it is desirable to increase system linearity in the presence of strong on or off channel signals in order to avoid creating intermodulation (IM) products in the desired signal passband. Typically, system linearity can be improved by reducing gain before reaching the IM limiting stages. For some systems, it is desirable to use amplifiers with continuously variable gain to optimize the required gain reduction. At best, many of these continuously variable gain amplifiers have constant third order intercept (IM.sup.3) over their gain control range, and at the worst, the third order intercept degrades with increasing attenuation.
The gain controllable amplifiers are usually placed near the front of a radio frequency (RF) or intermediate frequency (IF) string in the receiver thus allowing for system intermodulation improvements when gain is decreased. For large signals that require large amounts of gain reduction, the adjustable gain amplifier often becomes the limiting factor for the receiver's IM performance. In these circumstances, the designer of the stage would need to design an amplifier having sufficient IM performance required for strong signal conditions. Those skilled in high frequency circuit design will recognize the need for larger current drain for higher IM performance. This results in excess current drain for weak signal conditions when high linearity is not as important.
Thus, the need exists to provide a low noise amplifier (LNA) system topology such that a decreased amount of dynamic range is required by the LNA thereby requiring a lesser amount of current drain. This had the overall effect of providing a more efficient amplifier capable of handling a wide range of signal levels with relatively small current drain when integrated into a receiver IC package.